C Program to Compare Two Binary Files

This C Program compares two binary files, printing the first byte position where they differ.

Here is source code of the C Program to compare two binary files, printing the first byte position where they differ. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C Program to Compare two Binary Files, Printing the First Byte

```
 * Position where they Differ
```
```
 */
```
```
#include <stdio.h>
```
```
 
```

void compare_two_binary_files(FILE *,FILE *);

```
 
```
```
int main(int argc, char *argv[])
```
```
{
```
```
    FILE *fp1, *fp2;
```
```
 
```
```
    if (argc < 3)
```
```
    {
```

        printf("\nInsufficient Arguments: \n");

        printf("\nHelp:./executable <filename1> <filename2>\n");

```
        return;
```
```
    }
```
```
    else
```
```
    {
```
```
        fp1 = fopen(argv[1],  "r");
```
```
        if (fp1 == NULL)
```
```
        {
```

            printf("\nError in opening file %s", argv[1]);

```
            return;
```
```
        }
```
```
 
```
```
        fp2 = fopen(argv[2], "r");
```
```
 
```
```
        if (fp2 == NULL)
```
```
        {
```

            printf("\nError in opening file %s", argv[2]);

```
            return;
```
```
        }
```
```
 
```

        if ((fp1 != NULL) && (fp2 != NULL))

```
        {
```

            compare_two_binary_files(fp1, fp2);

```
        }
```
```
    }
```
```
}
```
```
 
```
```
/*
```

 * compare two binary files character by character

```
 */
```

void compare_two_binary_files(FILE *fp1, FILE *fp2)

```
{
```
```
    char ch1, ch2;
```
```
    int flag = 0;
```
```
 
```

    while (((ch1 = fgetc(fp1)) != EOF) &&((ch2 = fgetc(fp2)) != EOF))

```
    {
```
```
        /*
```

          * character by character comparision

          * if equal then continue by comparing till the end of files

```
          */
```
```
        if (ch1 == ch2)
```
```
        {
```
```
            flag = 1;
```
```
            continue;
```
```
        }
```
```
        /*
```

          * If not equal then returns the byte position

```
          */
```
```
        else
```
```
        {
```

            fseek(fp1, -1, SEEK_CUR);

```
            flag = 0;
```
```
            break;
```
```
        }
```
```
    }
```
```
 
```
```
    if (flag == 0)
```
```
    {
```

        printf("Two files are not equal :  byte poistion at which two files differ is %d\n", ftell(fp1)+1);

```
    }
```
```
    else
```
```
    {
```

        printf("Two files are Equal\n ", ftell(fp1)+1);

```
    }
```
```
}
```

$ gcc file15.c
$ a.out /bin/chgrp /bin/chown
Two files are not equal :  byte poistion at which two files differ is 25
 
/*
 * Verify using cmp command
 */
$ cmp /bin/chgrp /bin/chown
/bin/chgrp /bin/chown differ: byte 25,  line 1
 
$ a.out a.out a.out
Two files are Equal
/*
 * Verify using cmp command
 */
$ cmp a.out a.out

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